This invention relates to automatic pencils having an outer tubular casing housing an inner tube which receives a plurality of aligned sharpened leads and which has a bottom split end to clamp the bottommost lead during writing. More particularly, the invention relates to the construction of a lead pushing member and means for supporting the lead pushing member provided in the outer casing.
Various improvements have been made in the art for the performance and the simplicity of assembly of the automatic pencil. U.S. Pat. No. 4,320,982 discloses a mechanical pencil which has an outer casing with a tapered lower end whose inner side is provided with two diametrically opposed projections T to retain a bottommost coil of spring S as shown in FIGS. 1A to 1D. In the outer casing is an inner tube for holding sharpened pencil lead members. The spring S has a bottom end extending downward from the bottommost coil to form a lead pushing member S1 which is arranged to extend into the groove H of the clamping split end of the inner tube. Upon frequent upward and downward movement of the inner tube, the lead pushing member moves away from its proper location or moves out of the groove H, as shown in FIGS. 1A to 1D. This is because the spring retaining projections T support the spring at only two locations and the bottommost coil of the spring S and the lead pushing member are therefore liable to disclose. In addition, during assembly, the lead pushing member may be mislocated on one of the projections by which the lead pushing member will be pushed away from the groove H of the split end S1.
To alleviate the above disadvantage, the inventor of the present invention proposed an improvement in the construction of the outer casing which is illustrated in FIGS. 2A and 2B, in which the cone-shaped lower portion of the outer casing A is provided with an annular shoulder a1, a groove a2 and a restricted through-hole a3. The bottommost coil of the spring is seated on the shoulder a1, and the upper portion of the lead pushing member is received in the positioning groove to avoid lateral movement of the lead pushing member. However, it is found that the need to receive the lead pushing member in the groove a2 has created difficulties in the assembly of the pencil.